Various arrangements have been used in the past to control the pitch of a bulldozer blade during angling and tilting thereof. In some of these arrangements, the bulldozer blade is prohibited from pitching during tilting consequently inducing high pressures in the angling cylinders and/or high stresses in the structure itself. It is advantageous to provide an arrangement that would be simple in construction and would also allow for retrofitting of the mechanism on existing bulldozer blade arrangements. Furthermore, in some of the mounting arrangements currently used there is no provision for compensating for manufacturing tolerances that exist during assembly of the various components.
U.S. Pat. No. 3,631,930 which issued on Jan. 4, 1972 to Robert A. Peterson teaches a bulldozer blade mounting arrangement having a C-frame which is pivotably connected at the ends thereof to opposite sides of a tractor and having the lower rear center of the bulldozer blade connected to the front mid portion of the C-frame by a universal connection. The blade angling and pitching of this arrangement is controlled by a pair of hydraulic jacks connected to the C-frame and connected at respective locations to the back of the bulldozer blade thus providing a simplified three point mounting of the blade to the C-frame. The tilting of the blade relative to the C-frame is accomplished by a hydraulic cylinder connected to the central portion of the C-frame vertically disposed from the universal connection and to one side of a rear portion of the bulldozer blade. In this arrangement, the pitching of the blade is solely controlled by the angle cylinders. However, if the angling cylinders would happen to drift or get out of phase due to air in the cylinders or the lines, or due to oil seepage around the piston of the cylinder, the blade could pitch forwardly or rearwardly during operation and unnecessarily affect the bulldozing capability of the bulldozer blade.
In order to correct the above-noted problem of having no positive pitch control, others have provided various forms of positive retention pitch controls. For example, U.S. Pat. No. 3,991,832 which issued Ju1y 14, 1975 to Phillip Clinton Cooper discloses a bulldozer arrangement quite similar to that noted above relative to U.S. Pat. No. 3,631,930. In this arrangement, the lower rear central portion of the bulldozer blade is connected to a front central portion of a C-frame by a universal connection. The angling of the bulldozer blade is accomplished by a pair of cylinders connected between either side of the C-frame and the opposed ends of the bulldozer blade. The tilting of the blade is accomplished by a tilt cylinder connected between the C-frame and one end of the bulldozer blade in a vertically spaced relation to the universal connection. Furthermore, in this arrangement a positive pitch retention control is provided. This pitch control includes a bracket assembly secured to the back top central portion of the bulldozer blade and has a groove included therein and a slide member that is attached to the top central portion of the C-frame and is slidably disposed in the groove to ensure that the blade is not allowed to pitch any during tilting thereof. Since this arrangement does not allow the blade to pitch at all during tilting thereof, extra high forces are subjected to the angling cylinders consequently creating high pressure levels in the angling cylinders. In order to overcome this problem, a specialized relief arrangement was provided in the hydraulic circuitry to offset the high pressure levels that were being induced. Furthermore, this arrangement requires close control during manufacturing thereof to offset any manufacturing tolerances which may create binding thereof during assembly.
U.S. Pat. No. 4,424,871 which issued May 17, 1982 to Douglas B. Stickney teaches an improvement to minimize or avoid the high pressure levels which were induced in the angling cylinders of the above-noted U.S. Pat. No. 3,991,832. In this arrangement, as in the previous patents, the bulldozer blade is connected to a C-frame by a universal connection and the angling of the blade is controlled by two angling cylinders while the tilting thereof is controlled by a tilt cylinder connected between an upper portion of the C-frame and the backside of the bulldozer blade. This arrangement also includes a positive pitch control mechanism that does not allow the blade to pitch during tilting thereof. This arrangement includes a bracket having a groove therein secured to the C-frame and another bracket secured to the blade having a follower disposed in the groove of the first bracket to positively prohibit the blade from pitching during tilting thereof. In order to offset the high pressures that normally would be subjected to the angling cylinders during tilting, special efforts were made to connect the angling cylinders to the C-frame in a precise arrangement such that the points of connection of the angling cylinders to the C-frame falls in a straight line with the center of the universal joint. This arrangement requires a more precise control during manufacturing to correctly position the angling cylinders and would not allow ready retrofitting of the mechanism to an existing bulldozer blade mounting arrangement.
Canadian Pat. No. 1,115,514 which issued on Jan. 5, 1982 to Yokoyama et al teaches another arrangement for positively controlling the pitch of the bulldozer blade during angling and tilting thereof. In this mounting arrangement, the rear lower central portion of the bulldozer blade is connected to a front central portion of a C-frame by a universal joint. The angling of the bulldozer blade is controlled by a pair of angling cylinders connected between opposite sides of the C-frame and opposed end portions of the bulldozer blade while the tilting is controlled by a cylinder connected to the central upper portion of the C-frame and the back side of the bulldozer blade in a vertically spaced relation to universal connection. The positive pitch control in this arrangement is accomplished by a link or rod connected between a bracket on the top central portion of the bulldozer blade and a bracket on the top central portion of the C-frame. In this arrangement the rod connections do not have any built-in looseness. During tilting of the blade in this subject arrangement, the blade will automatically pitch as determined by the length of the rod which securely interconnects the C-frame and the bulldozer blade. If the length of the rod was not precise and accurately positioned, the blade would not be allowed to pitch in a normal manner. Consequently, in order to offset any high pressures in the angling cylinders or stresses in the mounting arrangement the length of the rod would have to be closely controlled and accurately positioned. Therefore, it would also inhibit the ability of easily retrofitting this arrangement to current bulldozer blade mounting arrangements that do not have a positive pitch retention mechanism.
The present invention is directed to overcoming one or more of the problems as set forth above.